Ball Screw Drive and Motor Vehicle Steering System Equipped with Same

Abstract

A ball screw drive includes a lead screw for converting an auxiliary torque produced by an electric motor into an auxiliary translational force which acts on a steering rack in the steering system of a motor vehicle. One end of the lead screw and one end of the steering rack are each connected to a track rod via an axial link, and the ball screw drive has a ball nut mounted in a housing with a fixed bearing. In order to withstand lateral loads or lateral forces coming from the track rod or rods and acting in the radial direction, there is provided between an end of the lead screw connected to the track rod and the ball screw drive a plain bearing element which supports the lead screw radially against the housing.

1 . A ball screw drive comprising:
 a threaded spindle configured to convert an assistance torque generated by an electric motor into a translational assistance force which acts on a toothed rack in a steering system of a motor vehicle, one end of the threaded spindle and one end of the toothed rack connected in each case by an axial joint to a track rod;   a ball nut mounted in a housing by a bearing; and   a plain bearing element arranged between the one end of the threaded spindle connected to the track rod and the toothed rack, the plain bearing element configured to support the threaded spindle radially with respect to the housing.   
     
     
         2 . The ball screw drive as claimed in  claim 1 , wherein:
 the plain bearing element includes a plain bearing bushing surrounding the threaded spindle, and   the plain bearing bushing is mounted cardanically in the housing so as to be pivotable at least about a transverse axis which is oriented perpendicular to a direction in which a transverse force component of a track rod force arises.   
     
     
         3 . The ball screw drive as claimed in  claim 2 , wherein the plain bearing bushing has a convexly curved ring-shaped outer circumference. 
     
     
         4 . The ball screw drive as claimed in  claim 3 , wherein:
 at least a first subregion of the outer circumference of the plain bearing bushing bears against a concavely curved inner wall, of the housing.   
     
     
         5 . The ball screw drive as claimed in  claim 2 , wherein:
 at least a second subregion of the outer circumference of the plain bearing bushing bears against a concavely curved inner wall of a ring, and   the ring is insertable into the housing.   
     
     
         6 . The ball screw drive as claimed in  claim 5 , wherein the ring is fixed in a desired position by a fixing element. 
     
     
         7 . The ball screw drive as claimed in  claim 2 , wherein:
 a first round-wire ring secures a first end of the plain bearing bushing against displacement in an axial direction, and   a second round-wire ring secures a second end of the plain bearing bushing against displacement in the axial direction.   
     
     
         8 . The ball screw drive as claimed in  claim 7 , wherein an outer circumference of the plain bearing bushing has two grooves in which the first and second round-wire rings are received. 
     
     
         9 . The ball screw drive as claimed in  claim 7 , wherein:
 the first end of the plain bearing bushing has a first bevel, and   the second end of the plain bearing bushing has a second bevel.   
     
     
         10 . A steering system with electrical power steering assistance for a motor vehicle comprising:
 a track rod;   a toothed rack;   an electric motor; and   a ball screw drive including
 a threaded spindle configured to convert an assistance torque generated by the electric motor into a translational assistance force which acts on the toothed rack, one end of the threaded spindle and one end of the toothed rack connected in each case by an axial joint to the track rod, 
 a ball nut mounted in a housing by a bearing, and 
 a plain bearing element arranged between the one end of the threaded spindle connected to the track rod and the toothed rack, the plain bearing element configured to support the threaded spindle radially with respect to the housing. 
   
     
     
         11 . A plain bearing element for a ball screw drive including a threaded spindle, the plain bearing element comprising:
 a housing; and   a plain bearing bushing surrounding the threaded spindle and mounted in the housing, the plain bearing bushing configured to support the threaded spindle radially with respect to the housing.